All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
A man's being a husband of a woman's sister or paternal or maternal aunt does not render him a Mahram for her. Therefore, it is impermissible for a woman to uncover her hair before these men, travel with them as Mahrams or do anything else that is only permissible to do with Mahram men.
Allaah Knows best.